The present invention relates to a transparent conductive layered structure having a transparent substrate and a transparent conductive layer and transparent coating layer formed in succession on this substrate that is used in the front panel, etc., of CRT, etc., displays. In particular, it relates to a transparent conductive layered structure with excellent film strength, weather resistance, conductivity, etc., of the transparent conductive layers and with which a reduction in production cost is expected, and method of producing the same, a coating liquid for forming a transparent coating layer and a coating liquid for forming a transparent conductive layer used in this production method, and a display that uses the transparent conductive layered structure.
In addition to being able to easily see the display screen and thereby preventing visual fatigue, today there is a demand for cathode ray tubes (CRTs), which are used as computer displays, etc., with which there is no adhesion of dust or electrical shock due to electrostatic charge of the CRT screen.
Furthermore, in recent years there has been concern over the detrimental effects of low-frequency electromagnetic waves generated from CRTs on the human body and it is preferred that these types of electromagnetic waves not be leaked to the outside.
Moreover, problems with the same electrostatic charge and leakage of electromagnetic waves as with CRTs have recently been pointed out with plasma display panels (PDPs) used in wall-mounted televisions.
It is possible to prevent this leakage of electromagnetic waves by, for instance, forming a transparent conductive layer on the front panel of the display.
The above-mentioned method of preventing the above-mentioned leakage of electromagnetic waves is theoretically the same as countermeasures that have recently been taken to prevent electrostatic charge. However, the above-mentioned transparent conductive layer must have a much higher conductivity than conductive layers that are formed for prevention of electrostatic charge (as high as 108 to 1010 xcexa9/xe2x96xa1 in terms of surface resistance).
That is, it is necessary to form a transparent conductive layer with at least as low a resistance as 106 xcexa9/xe2x96xa1 (ohm per square) or less, preferably 5xc3x97103 xcexa9/xe2x96xa1 or less, particularly 103 xcexa9/xe2x96xa1 or less, in order to prevent leakage of electromagnetic waves (electric shielding) of CRTs, and a resistance of, for instance, 10 xcexa9/xe2x96xa1 or less is needed in PDPs.
Moreover, thus far there have been several suggestions for dealing with the above-mentioned electric shielding. For instance,
(1) the method of applying and drying a coating liquid for forming a transparent conductive layer of conductive oxide microparticles, such as indium tin oxide (ITO), etc., or metal microparticles dispersed in a solvent on the front panel of a CRT and then baking this at a temperature of about 200xc2x0 C. to form the above-mentioned transparent conductive layer,
(2) the method of forming a transparent conductive tin oxide film (NESA film) on the above-mentioned panel surface by high-temperature chemical vapor deposition (CVD) of tin chloride,
(3) the method of forming a transparent conductive film of indium tin oxide and titanium oxynitride on a front panel by sputtering, and the like have been presented for CRTs.
Moreover,
(4) the method of forming a conductive film by placing a conductive mesh made of metal or metal-coated fibers on the device body side of a front panel of a PDP,
(5) the method whereby a transparent conductive film made by sputtering of a metal such as silver, etc., is formed on the above-mentioned panel and the like have been presented for PDPs.
However, there is a problem with method (4) for PDPs in that since a conductive mesh is used, surface resistance is low and transmittance is also low. There is also a problem in that a moirxc3xa9 pattern is produced and a problem in that the process for forming a conductive film is complex and cost is high.
In contrast to this, method (1) for CRTs is much simpler and production cost is lower than methods (2), (3) and (5) whereby a transparent conductive film is formed by CVD or sputtering and therefore, the method under (1) that uses a coating liquid for forming a transparent conductive layer is very advantageous for the above-mentioned CRTs as well as for PDPs.
However, the surface resistance of the film that is obtained is high at 104 to 106 xcexa9/xe2x96xa1 and is not sufficient for blocking leakage of an electric field with a coating liquid for forming a transparent conductive layer that uses conductive oxide microparticles, such as indium tin oxide (ITO), etc., by method (1).
On the other hand, transmittance of the film obtained using a coating liquid for forming a transparent conductive layer using metal microparticles is low in comparison to coating liquid that uses ITO because the metal microparticles are not light transmitting. However, since the metal microparticle layer takes on a network structure during film formation after application, the reduction in the above-mentioned transmittance is small and a low resistance film of 102 to 103 xcexa9/xe2x96xa1 is obtained. Therefore, it is considered to be a method with good prospects for the future.
Moreover, the metal microparticles that are used for the above-mentioned coating liquid for forming a transparent conductive layer are limited to noble metals, such as silver, gold, platinum, rhodium, palladium, etc., which rarely oxidize in air, as shown in Japanese Laid-Open Patent No. Hei 8-77832 and Japanese Laid-Open Patent No. Hei 9-55175. This is because when metal microparticles other than a noble metal, such as iron, nickel, cobalt, etc., are used, an oxide film always forms on the surface of these metal microparticles in an air ambient atmosphere and good conductivity as a transparent conductive layer is not obtained.
Furthermore, when specific resistance of the above-mentioned silver, gold, platinum, rhodium, palladium, etc., is compared, the specific resistance of platinum, rhodium and palladium is high at 10.6, 5.1, and 10.8 xcexcxcexa9xc2x7cm, respectively, when compared to the 1.62 and 2.2 xcexcxcexa9xc2x7cm of silver and gold. Therefore, the use of gold particles and silver particles is preferable for forming a transparent conductive layer with low surface resistance. Consequently, silver microparticles and gold microparticles, etc., are mainly used as the above-mentioned metal microparticles.
However, when silver microparticles are used, there is a problem with weather resistance in that there is marked sulfurization, oxidation and degradation by brine, ultraviolet rays, etc., and therefore, gold-containing noble metal microparticles, such as gold-coated silver microparticles where the surface of silver microparticles is coated with gold, etc., and alloy microparticles, etc., made from gold and a noble metal other than gold (such as silver, etc.), have also been presented.
On the other hand, anti-glare treatment is performed for instance, on the front panel surface of CRTs in order to prevent reflection on the screen in order to make the display screen easy to see. This anti-glare treatment is done by the method whereby diffused reflection at the surface is increased by making fine irregularities in the surface. However, it cannot be said that this method is very desirable because image quality drops due to a reduction in resolution when it is used. Consequently, it is preferred that, instead, anti-glare treatment by the interference method be performed whereby the index of refraction of the transparent film and film thickness are controlled so that there is destructive interference of reflected light on incident light. In order to obtain low-reflection results by this type of interference method, a 2-layered film is generally used wherein optical film thickness of a film with a high index of refraction and a film with a low index of refraction is set at xc2xcxcex and xc2xcxcex, respectively, or xc2xdxcex and xc2xcxcex, respectively. Film consisting of the above-mentioned indium tin oxide (ITO) microparticles is also used as this type of film with a high index of refraction.
Furthermore, of the optical constants of metals (nxe2x88x92ik, n: index of refraction, i2=xe2x88x921, k: extinction coefficient), the value of n is small, but the value of k is very high when compared to ITO, etc., and therefore, even if a transparent conductive layer consisting of metal microparticles is used, the same anti-reflection results as with ITO are obtained by interference with light by the 2-layered film.
However, since gold is chemically inert, there is a problem with transparent conductive layers formed by a coating liquid for forming a transparent conductive layer that uses the above-mentioned gold microparticles or gold-containing noble metal microparticles as the metal microparticles in that it is difficult to strengthen the bond between these gold microparticles or gold-containing noble metal microparticles and a binder matrix of silicon oxide, etc., and therefore, film strength and weather resistance of the transparent conductive layers that are formed are insufficient.
The present invention focuses on these problems, its object being to present a transparent conductive layered structure with excellent film strength, weather resistance, conductivity, etc., of the transparent conductive layers.
Another object of the present invention is to present a method of producing a transparent conductive layered structure with excellent film strength, weather resistance, conductivity, etc., of the transparent conductive layers.
Yet another object of the present invention is to present a coating liquid for forming a transparent coating layer that can be used in the above-mentioned method of producing a transparent conductive layered structure.
Moreover, another object of the present invention is to present a coating liquid for forming a transparent conductive layer that can be used in the above-mentioned method of producing a transparent conductive layered structure.
Furthermore, another object of the present invention is to present a display with which surface reflection of the display screen is controlled and there is a long-term high electric shielding effect.
That is, the present invention is a transparent conductive layered structure, comprising a transparent substrate, a transparent conductive layer, and a transparent coating layer, wherein the transparent conductive layer and transparent coating layer are formed in succession on this transparent substrate, and the main components of the above-mentioned transparent conductive layer are gold microparticles or gold-containing noble metal microparticles containing 5 wt % or more of gold with a mean particle diameter of 1 to 100 nm and a binder matrix comprising at least one functional group selected from mercapto groups (xe2x80x94SH), sulfide groups (xe2x80x94Sxe2x80x94), and polysulfide groups (xe2x80x94Sxxe2x80x94, Xxe2x89xa72).
In addition, the first method of producing this transparent conductive layered structure comprises the steps of applying a coating liquid for,forming a transparent conductive layer, whose main components are a solvent and gold microparticles or gold-containing noble metal microparticles containing 5 wt % or more of gold with a mean particle diameter of 1 to 100 nm dispersed in this solvent, to a transparent substrate, then applying a coating liquid for forming a transparent coating layer, whose main components are a functional group-containing compound having at least one functional group selected from mercapto groups (xe2x80x94SH), sulfide groups (xe2x80x94Sxe2x80x94), and polysulfide groups (xe2x80x94Sxxe2x80x94, Xxe2x89xa72), a binder and a solvent, and performing heat treatment.
Moreover, the second production method comprises the steps of applying a coating liquid for forming a transparent conductive layer, whose main components are a solvent and gold microparticles or gold-containing noble metal microparticles containing 5 wt % or more of gold with a mean particle diameter of 1 to 100 nm and a functional group-containing compound having at least one functional group selected from mercapto groups (xe2x80x94SH), sulfide groups (xe2x80x94Sxe2x80x94), and polysulfide groups (xe2x80x94Sxxe2x80x94, Xxe2x89xa72) dispersed in this solvent, to a transparent substrate, then applying a coating liquid for forming a transparent coating layer whose main components are a binder and a solvent, and performing heat treatment.
Next, the coating liquid for forming the transparent coating layer used in the above-mentioned first production method comprises as its main components a solvent, a binder, and a functional group-containing compound having at least one functional group selected from mercapto groups (xe2x80x94SH), sulfide groups (xe2x80x94Sxe2x80x94), and polysulfide groups (xe2x80x94Sxxe2x80x94, Xxe2x89xa72), wherein the mixture ratio of the binder and the functional group-containing compound is 0.1 to 50 parts by weight functional group-containing compound per 100 parts by weight binder.
Moreover, the coating liquid for forming the transparent conductive layer used in the second production method comprises as its main components a solvent and gold microparticles or gold-containing noble metal microparticles containing 5 wt % or more of gold with a mean particle diameter of 1 to 100 nm and a functional group-containing compound having at least one functional group selected from mercapto groups (xe2x80x94SH), sulfide groups (xe2x80x94Sxe2x80x94), and polysulfide groups (xe2x80x94Sxxe2x80x94, Xxe2x89xa72) dispersed in this solvent.
Furthermore, the above-mentioned display device comprises a display body and a front panel that has been placed on the front of the same body, wherein the above-mentioned transparent conductive layered structure is used as the above-mentioned front panel with the transparent 2-layered film side of the same on the outside.